Less than a month into a difficult start for the Trump presidency, numerous Democrats have been talked up as possible 2020 candidates, including the party's most recent standard bearer, Hillary Clinton. Clinton has already been in the news as a talked-about NYC mayoral contender and received significant coverage after she chided Trump on twitter. But anyone looking for a Clinton comeback should slow down. History shows that there is good reason to think the Democrats will look elsewhere.

This may not be obvious from a quick look at the record. If Clinton ran and won, she would join a long line of presidential comebacks. Starting with Thomas Jefferson, who lost the 1796 race before winning in 1800 to a George H.W. Bush, a loser in 1980 before winning in 1988, a quarter of U.S. presidents failed in their first attempt to be president before finally entering the White House.

Most of those candidates never actually received the party's nomination in their initial run for office. Ronald Reagan and George H.W. Bush both came in second in their first attempts for the presidency. Being a major party nominee who gains the nomination a second time is a much harder road for candidates. Richard Nixon, the Republican candidate in 1960, was the last to pull off this feat. Before that, Adlai Stevenson and Thomas Dewey both managed to lose a presidential race twice. Going back a little further, William Jennings Bryan managed this trick thrice.

"Unlike in 2016, other big name Democratic candidates are not going to decline to run in order to clear the way for Clinton. Democrats who are considering runs, like Elizabeth Warren, Cory Booker, Andrew Cuomo, are unlikely to give up their chance at the presidency."

The timing of these return nominees shows the challenges that Clinton would face. They all took place before the modern primary and caucus system. For these earlier nominees, they only needed the support of the existing political figures at the national conventions. Since the primary and caucus system has taken hold, no politician has ever really tried to make a comeback. Mitt Romney had a high-profile flirtation last year before backing down. In years past, there was discussion about comebacks from Gerald Ford, Al Gore and John Kerry, but in each case the candidate pulled back.

It may be that being a losing candidate may have a larger negative implication for voters than for the politically connected conventioneers of old. The conventions involved significant horse-trading and a well-respected and known name would have the ability to unify the party.

Modern voters have a different standard. They are focused on winners and, as we've seen, are quick to cast away the failed candidates. In this sense, Clinton has a serious problem. She will likely be blamed for failing to triumph in easily winnable races. She was the front-runner in 2008 before being overtaken by Barack Obama. While the primary field was cleared in 2016, she was unable to put Bernie Sanders away until the last moment, sustaining significant damage to her plan for an easy race. And she was seen as the heavy favorite in November. Her campaign strategy — notably her ignoring the key Midwest states — is seen as partly to blame for the shocking defeat.

Unlike in 2016, other big name Democratic candidates are not going to decline to run in order to clear the way for Clinton. Democrats who are considering runs, like Elizabeth Warren, Cory Booker, Andrew Cuomo, are unlikely to give up their chance at the presidency. Donors, who may have withheld support from primary challengers in 2016, will not be so shy in 2020. And Barack Obama and the Democratic National Committee will no longer be giving their tacit or active support in a primary race.

One other fact to consider is that unlike Republicans, who frequently choose past candidates as their own nominee, modern Democrats shun candidates who previously ran for president. Since 1968, only Hillary Clinton and Al Gore — who had a huge advantage after serving as vice president — ran for the nomination before winning it.

Hillary Clinton's supporters may want to keep their fires burning for a rematch against Donald Trump. They could be looking at past candidates who accomplished this comeback. But recent events show that they have a significant challenge if Clinton wants to take a third run for the White House. Modern presidents don't seem to get two chances in one lifetime.

Commentary by Joshua Spivak, a senior fellow at the Hugh L. Carey Institute for Government Reform at Wagner College in New York. He blogs at The Recall Elections Blog. Follow him on Twitter @recallelections.

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